In a packet transport network, information is exchanged between nodes by a routing/signaling protocol and the route of a packet to be transported is controlled. For example, in a network using MPLS (multi-protocol label switching) as its core, its reachability to each node is checked by a routing protocol, such as OSPF (open shortest path fast) or the like, sometimes traffic engineering information (for example, a free band, etc.) is exchanged and packet transport tunnel labels are distributed by a signaling protocol, such as an LDP (label distribution protocol), a RSVP-TE (resource reservation protocol traffic extension) or the like. Then, in a service for emulating an Ethernet line (called VPWS and VPLS in the cases of point-to-point and multi-point services, respectively; see RFC4447 and RFC4762 for VPWS and VPLS, respectively), labels for identifying an emulated line are distributed using a LDP (label distribution protocol) between MPLS edge nodes (PE (provider edge, so-called gateway), are attached to (capsuled into) the Ethernet frame of a client together with tunnel labels for transporting the MPLS network and are transported. The emulated (virtual) line built thus is called PW (pseudo wire).
FIG. 1 explains a redundant edge node.
A redundant node can be realized at high speed and efficiently by a public technology, such as fast re-route or the like, within a VPLS core network. However, in order to provide higher availability, as in RFC4762, a client location is accommodated in a plurality of redundant PEs and a connection method for specifying one PE and the others as primary and secondary, respectively, is required. In communications between client locations CE, a transmitting destination and a transmitting source are specified by an MAC address. However, communications between edge nodes are routed by a label for specifying a PW and a tunnel.
However, in the case of the prior art, since it is necessary to keep a secondary PW, twice PWs are required for point-to-point communications and four times of PWs as that at the time of a non-redundancy are required for the entire network in order to promote a redundant edge node in a full-mesh connection (of it, ¾ is not normally used). Furthermore, the load of the update process of a route information table at the time of a primary system failure (MAC table flush for clearing the MAC learning table of a point-to-point PE in the case of VPLS) is a problem.
FIG. 2 explains the problems of the prior art. The upper section of FIG. 2 illustrates a state before a failure occurs. When a client location a, such as a computer or the like, communicates with other client locations b and c, such as computers or the like, it is assumed that the edge node PE A of a network is made redundant and a secondary edge node PE A′ is provided. Communications are normally conducted via a primary edge node PE A. At this time, tables in which output ports p1, pw-AB and pw-AC are related to MAC addresses a, b and c, respectively, are stored in the edge node PEA. The MAC address a is the MAC address of the location a. The MAC addresses b and c are the MAC addresses of the locations b and c, respectively. In this case, a PW is formed in order to transport a packet from the edge node PE A to edge nodes PE B and PE C. This is a primary PW. However, although the edge node PE A′ is not normally used, it is necessary to set another PW from the edge node PE A′ to the edge nodes PE B and PE C as a secondary PW.
Then, when a failure occurs in a primary PE, as illustrated in the lower section of FIG. 2, the edge node PE A transmits the erase message of MAC address (in the case of FIG. 2, the MAC address a since a port accommodating the location a fails) of a failed location to the opposing node edges PE B and PE C. Then, the MAC address a is erased from the MAC tables of the edge nodes PE B and PE C. Simultaneously, when receiving an Ethernet frame from the location a (accompanying a failure between the location a and the PE A), the edge node PE A′ learns the transmitting source MAC address a and also start communications using a PW provided in advance. Since the PE B and PE C receive the Ethernet frame from another PW, they learn the MAC again.
As clear from this, when making an edge node redundant, since it is necessary to set a PW to a secondary edge node, many network sources are consumed.
Patent document 1 discloses a technology for attaching respective peculiar MAC addresses and IP addresses and also a common virtual MAC address and a virtual IP address to operating and waiting servers in an information configuration composed of operating and waiting systems.    Patent document 1: Japanese Laid-open Patent Publication No. 2005-136690